Tibiofemoral articulation and axial tibial rotation of the knee after a cruciate retaining total knee arthroplasty

Numerous research has reported that total knee arthroplasty (TKA) cannot reproduce axial tibial rotations of normal knees. The objective of this study was to measure the tibiofemoral articular contact motions and axial tibial rotations of TKA knees to investigate the mechanism causing the knee kinematics change of after TKAs. Eleven patients with unilateral cruciate retaining (CR) TKA were tested for measurements of knee motion during a weight-bearing flexion from 0° to 105° using an imaging technique. The tibiofemoral contact kinematics were determined using the contact points on medial and lateral surfaces of the tibia and femoral condyles. Axial tibial rotations were calculated using the differences between the medial and lateral articulation distances on the femoral condyles and tibial surfaces at each flexion interval of 15°. On femoral condyles, articular contact distances are consistently longer on the medial than on the lateral sides (p < 0.05) up to 60° of flexion, corresponding to internal tibial rotations (e.g., 1.3° ± 1.0° at 15–30° interval). On tibial surfaces, the articular contact point on the medial side moved more posteriorly than on the lateral side at low flexion angles, corresponding to external tibial rotations (e.g., −1.4° ± 1.8° at 15–30° interval); and more anteriorly than on the lateral sides at mid-range flexion, corresponding to internal tibial rotations (e.g., 0.8° ± 1.7° at 45–60° interval). At higher flexion, articular motions on both femoral condyles and tibial surfaces caused minimal changes in tibial rotations. These results indicate that the axial tibial rotations of these TKA knees were mainly attributed to asymmetric articulations on the medial and lateral femoral condyles and tibial surfaces. The data can help understand the mechanisms causing axial tibial rotations of TKA knees and help improve implant designs for restoration of normal knee kinematics.